On the recent mobile telephone market, models of mobile telephones having built-in camera modules have been becoming dominant. These camera modules need to be embedded in the mobile telephones. Therefore, the camera modules face greater demands for being compact and lightweight, as compared with camera modules to be embedded in digital cameras.
Among such camera modules, there have been an increasing number of camera modules that (i) achieve their autofocus (AF) functions with the use of lens drive devices and (ii) are mounted on electronic devices such as mobile telephones. Various types of lens drive devices have been developed so far, and examples of the lens drive devices encompass those employing stepper motors, those employing piezoelectric sensors, and those employing voice coil motors (VCM). Such lens drive devices have already been distributed on the market.
Further, mobile telephones have started to include a camera module having an optical image stabilizer (OIS) function. The OIS function is in wide public use in the field of digital cameras and video cameras. For mobile telephones, a size-related problem and the like have delayed the adoption of the OIS function until recent years.
Patent Literature 1 discloses an example lens driving device for an autofocus function. Specifically, the lens driving device disclosed in Patent Literature 1 is configured such that in a state where a current is not flown through a coil, a lens support is at an intermediate position between an infinity position and a maximum close position (macro). This configuration can reduce the distance of movement to a target position, and also reduce power consumption.
In a case where lenses are fixed to a lens driving device in a camera module having an AF function, failing to properly set an initial position for the lenses with respect to an image pickup element in an optical axis direction causes defocusing, with the result of an out-of-focus image.
In view of that, the mainstream of conventional AF camera modules has a mechanism in which (i) a screw structure is provided for each of a lens barrel (that is, a casing containing an assembly of a plurality of lenses) and a lens holder and in which (ii) the position of the lenses is adjusted along the optical axis with use of the screw structures.
A focus adjustment mechanism involving the use of screws, however, poses various problems: For example, torque management for the screws is troublesome, and an optical tilt is undesirably increased depending on the accuracy of members including the screws. In view of this, Patent Literature 2 proposes a focus adjustment mechanism not involving use of screws.
Patent Literature 2 discloses a focus adjustment mechanism in which (i) no screw structure is provided between a lens barrel and a lens holder for a focus position adjustment and in which (ii) the lens barrel is slidable until it is fixed to the lens holder. With this structure, the lens barrel is positioned with respect to the lens holder with use of a jig, and is fixed to the lens holder. There is a slight gap between the lens holder and the lens barrel. With this gap, the tilt of the lens barrel is less likely influenced by the tilt of the lens holder. This configuration allows the lens barrel to be positioned with respect to the lens holder and fixed to the lens holder with the accuracy of the jig and with a low tilt.